The invention relates to an apparatus to change the force exerted on an actuator mechanism.
Such an apparatus is already known from the German Patent Publication DE-OS No. 17 76 078. On this apparatus, there are several control pistons operated by a pressure medium, which act directly on the actuator mechanism by means of their piston rods. The control pistons exhibit different effective surfaces. Thus, by the selection of the number of control pistons and/or the selection of the appropriate size of the effective surface which is acted on by the pressure medium, different forces can be produced, which are exerted by the control pistons on the actuator mechanism. In the known apparatus, the actuator mechanism is used to operate a pilot valve for a servo-motor. The restoring force acting on the actuator is the pressure controlled by the pilot valve.
Since the forces exerted by the control pistons on the actuator are a function of the pressure of the pressure medium acting on the control piston, the specified forces can only be achieved if a constant pressure of the pressure medium acting on the control pistons is maintained. This means that the precision of control of the forces exerted on the actuator is a function of the constancy of the above-mentioned pressure.